Thin image display devices as typified by displays, i.e., flat panel displays, have been released on the market because they are thinner than cathode-ray tube displays and they do not occupy much space in depth. Their market price has decreased year by year with advances in production techniques, resulting in a further increase in demand and a yearly increase in production. Especially, color LCD TVs have almost become the mainstream of TVs. Also in recent years, organic light-emitting display devices such as organic EL displays, which emit light by themselves and thereby have high visibility, have received attention as the next generation of image display devices. In relation to the performance of these image display devices, there is a strong demand for a further increase in image quality, such as an increase in contrast and color reproducibility, and a decrease in power consumption.
A color filter is used in these liquid crystal display devices and organic light-emitting display devices. For example, in the case of color LCDs, the amount of light is controlled by using a back light as the light source and electrically driving the liquid crystal. Colors are represented by the light that passed through the color filter. Accordingly, the color filter is indispensible for color representation in LCD TVs and plays a large role in determining display performance. In organic light-emitting display devices, a color image is formed in the same manner as liquid crystal display devices, when the color filter is used in combination with an organic, white light-emitting element.
A recent trend is that there is a demand for power-saving image display devices. To increase backlight use efficiency, there is a very high demand for high-luminance color filters. This is a major issue especially for mobile displays such as mobile phones, smart phones and tablet PCs.
Even though technological advances have increased battery capacity, there is still a limit on battery capacity of mobile devices. Meanwhile, there is a trend that power consumption has grown with the increase in screen size. Image display devices containing a color filter determine the design and performance of mobile terminal devices because they are directly linked to the usable time and charging frequency of mobile terminal devices.
In general, a color filter has a transparent substrate, color layers made of color patterns of the three primary colors (red, green and blue), and a light shielding part formed on the transparent substrate so as to define each color pattern.
To form such color layers, a dispersion method in which pigments with excellent heat resistance and light resistance are used as colorants, has been widely used. However, it is difficult for color filters produced by use of pigments to satisfy the latest demand for higher luminance. As a result, in recent years, it has been considered to use dyes, which generally have higher transparency than pigments, or lake pigments, which are dyes made insoluble by a precipitant, in place of pigments (Patent Literatures 1 and 2). However, dyes and lake pigments are problematic in that they are inferior in heat resistance to pigments and the chromaticity is likely to change when they are heated at high temperature in color filter production process. Since dyes show particularly poor heat resistance when they are dissolved for use, it has been considered to disperse dyes for use (Patent Literature 3).
To satisfy the demand for higher contrast, it is requested to make these color materials finer at the time of dispersion. Once the color materials are made finer, the surface area is increased and creates a need to increase the amount of a dispersant added, in order to homogeneously disperse the color materials. However, once the amount is increased, although the color materials can be homogeneously dispersed, there is such a problem that alkaline developability of a photocurable resist composition thus formed is decreased and the photocurable resist composition, which is not subjected to exposure, remains on a substrate, or that the productivity and quality of the photocurable resist composition are reduced.
By using a phosphate-modified block or graft copolymer as a dispersant, which forms a salt with a specific acidic organophosphorous compound, the inventors of the present invention have developed a color resin composition which is good in dispersibility, able to form a color filter with high contrast, and excellent in alkaline developability (for example, see Patent Literatures 4 to 6).